"People ask me how I do research for my science fiction. The answer is, I never do any research. I just enjoy reading the stuff, and some of it sticks in my mind and fits into the stories."
- Frederik Pohl

A device that finds substantial masses, particularly in the path of a space craft.

As if in answer, a loud clangor came from the Orford mass detector, on the wall back of them. Dubold shut off the rockets, while Mansell leaped to the telescope. Dubold narrowed the detector beam to a tiny spear of electron stream, and turned to the screen. The feed-back of that narrowed beam would detect a tiny mass a thousand miles out in space through the disturbance of its flowing electrons and locate it in space as accurately as if sighted by a gun. At the intersection of the cross-bar lines a tiny shadow showed like a blot of ink in its intensity. Yet Mansell could see nothing..

Mansell changed the course of the ship slightly and the clangor ceased. Dubold shifted the needle beam a bit and located the mass again. A light- ning calculation by Mansell told them that the mass was at least fifteen hun- dred miles ahead. Its detection informed them that the mass was large enough to be seen with the naked eye. Yet Mansell could see nothing.

Mansell and Dubold looked at each other doubtfully, but Shafton was not watching them. Instead, he had his eyes glued to the gravitator as if he could not believe what he saw.

"Strange, I could see nothing," Mansell admitted to Dubold, in an under- tone. "Must be a phenomenon of space, something we don't understand. However, we are out of its path..."

fE looked toward Shafton as he spoke. A flicker of alarm crossed his sharp-cut features as his attention riveted upon the young spaceman's face. For Shafton's eyes were staring aghast into the gravitator's dial.

"The gravitator!" Shafton cried. "It has swung over to 10-x."

"Impossible," the commander snapped,"why—why, it is unthinkable. There must be something wrong." Suddenly he switched the floor magnets off. So sensitive were the spacemen's sensations to gravitational pulls out there in almost weightless space, a slight but decided tug toward the prow could be felt. Again the commander scanned the surrounding space.